Cardiac arrhythmias (e.g., fibrillation) are irregularities in the normal beating pattern of the heart and can manifest themselves in either the atria or the ventricles of the heart. For example, atrial fibrillation is a form of arrhythmia characterized by rapid randomized contractions of atrial myocardium, causing an irregular, often rapid ventricular response. The regular pumping function of the atria is replaced by a disorganized, ineffective quivering as a result of chaotic conduction of electrical signals through the upper chambers of the heart. Atrial fibrillation is often associated with other forms of cardiovascular disease, including congestive heart failure, rheumatic heart disease, coronary artery disease, left ventricular hypertrophy, cardiomyopathy, or hypertension.
It is now understood that recurrent atrial fibrillation (paroxysmal and persistent) is triggered by rapidly firing tissue, (called “ectopic foci”), that are principally located in one or more of the four pulmonary veins, which attach to the rear of the left atrium. It has been found that atrial fibrillation may be prevented by electrically isolating the pulmonary veins from the rest of the left atrium.
Various techniques have been employed for pulmonary vein isolation. A common purpose of each of these techniques is to replace cardiac muscle cells with scar tissue, which scar tissue cannot conduct normal electrical activity within the heart.
In one known approach, circumferential ablation of tissue surrounding the junction of the pulmonary veins and the left atrium has been practiced to treat atrial fibrillation. By ablating the heart tissue at this location transmurally and circumferentially, electrical conductivity between the pulmonary veins and the remainder of the left atrium can be blocked as a result of creating this scar or durable barrier, preventing the initiation of the fibrillatory process.
Several types of ablation devices have recently been proposed for creating lesions to treat cardiac arrhythmias. Many of the recently proposed ablation instruments are percutaneous devices that are designed to create individual lesions from within the heart. Such devices are positioned in the heart by catheterization of the patient, e.g., by passing the ablation instrument into the heart via a blood vessel, such as the femoral vein and then gaining transseptal access to the left atrium.
Typically, percutaneous devices are positioned with the assistance of a guide catheter, which is first advanced into the left side of the heart through a hole made in the intraatrial septum. In one increasingly common approach, a guide catheter or similar guide device is advanced through the vasculature and into the left atrium of the heart. A catheter instrument with an expandable element is then advanced through the guide catheter and into each one of the ostia of pulmonary veins where the expandable element (e.g., a balloon) is inflated. The balloon includes a moveable ablation element, e.g., an energy emitting device, such as a laser, disposed in the inner surface of the balloon, which allows the physician to sequentially position and control the application of energy in the area of the junction between the vein ostium and the left atrium to create a durable barrier which is the objective of the ablation procedure.
It is noted that ablation directed distally beyond the ostium or within the pulmonary vein itself can result in complications. Overtreatment deep within a vein can result in stenosis (closure of the vein itself), necrosis or other structural damage, any of which can necessitate further interventions. Conversely, undertreatment, in which the scar tissue formed is not continuous and/or insufficiently transmutural to replace the cardiac tissue sought to be durably electrically isolated from the atrium will cause the treatment ablation procedure to be unsuccessful. Thus, repeating of the treatment ablation procedure is then required which is almost always undesirable.
Currently, when laser energy has been applied to a region of tissue at an ostium of the PV there is no reliable visible change to that region of tissue when viewed through an endoscope thereby presenting the problem of distinguishing treated tissue (e.g., lesion) from de novo tissue.
The lesions are not visible for various reasons. For example, the ablation energy in these procedures typically penetrates deeply into the atrial tissue to create the lesion while leaving the appearance of the endocardial surface relatively unchanged. Additionally, color video cameras are often not sensitive enough to discriminate the subtle color changes that distinguish treated from untreated tissue. Also, the light levels delivered to the site are limited since they typically travel to the treatment site via a small optical fiber thereby further hindering the ability of video cameras to reliably visualize these distinctions.
Thus, there remains a need in the art for systems and methods configured to accurately and immediately confirm whether the pulmonary vein isolation procedure was successful, thereby allowing the user (electrophysiologist, more specifically an electrophysiologist or interventional cardiologist) to take corrective action in real time to ensure a complete circumferential barrier has been durably formed.